This entry is the integer number of theoretical trays (equilibrium stages) in the column model. Every column model (except single tray columns) must have at least two trays. See Single Tray Columns for additional details. There is no limit on the number of trays for a column model. Trays are always numbered from the top down. For distillation columns with condensers, the condenser is always defined as tray one even though it does not function as an equilibrium stage for subcooled condensers. For distillation columns with reboilers, the reboiler is defined as the highest numbered tray.
Usage
Enter the number of theoretical trays in the data entry field, with any reboiler and condenser counted as trays. For new columns the number of trays in the Column Configuration Window is automatically transferred to this field, but may be revised if desired.
In actual columns the trays usually produce less than perfect equilibrium separations, i.e., the tray efficiencies are less than 100 percent. Therefore you should apply an efficiency factor to the actual number of trays to determine the number of theoretical trays to use in the model. Efficiency factors are usually based on experience for the particular separation being modeled and the factors can vary in the various zones in the column. Note that such user applied efficiencies always result in a model with an integer number of trays, i.e., a fraction of an equilibrium stage is not possible.
Fractional trays may be considered for the Inside-Out, Enhanced I/O or Chemical algorithms by using the supplied tray efficiency models. These models may also be used to modify the efficiency for selected components in the column feed stream. The supplied tray efficiency models have limitations and you should thoroughly understand the concepts before using them in column models. None of these models correspond to "overall tray efficiencies" and it is often difficult to apply them to actual columns without trial and error adjustments.
Distillation Column Unit Operation - Technical Information
Liquid-Liquid Extraction Unit Operation - Technical Information